Vascular implant

ABSTRACT

A medical implant ( 20 ) includes first and second ring members ( 22, 24 ), each including a resilient framework ( 26 ) having a generally cylindrical form. A tubular sleeve ( 28 ) is fixed to the first and second ring members so as to hold the ring members in mutual longitudinal alignment, thereby defining a lumen ( 32 ) passing through the ring members. A constricting element ( 30 ) is fit around the sleeve at a location intermediate the first and second ring members so as to reduce a diameter of the lumen at the location.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/660,228, filed Jul. 26, 2017, entitled “VASCULAR IMPLANT, which is acontinuation of U.S. patent application Ser. No. 14/542,311, filed Nov.14, 2014, now U.S. Pat. No. 9,744,059, which issued on Aug. 29, 2017,which is a continuation of U.S. patent application Ser. No. 13/250,968,filed Sep. 30, 2011, now U.S. Pat. No. 8,911,489, which issued on Dec.16, 2014, which is a continuation of U.S. patent application Ser. No.10/595,926 filed Jul. 12, 2006, which is a U.S. National Stageapplication of International Application No. PCT/IL2004/0010 filed Nov.18, 2004, which claims priority to Israeli Patent Application No. 158960filed Nov. 19, 2003, incorporated herein by reference in its entiretyand to which application we claim priority under 35 USC § 120.

FIELD OF THE INVENTION

The present invention relates generally to implantable therapeuticdevices, and specifically to intravascular implants.

BACKGROUND OF THE INVENTION

Stent implants are commonly used in treating arterial stenoses and otherunwanted constrictions of body passages. Stents typically comprise ametal coil or mesh. An arterial stent, for example, is threaded throughthe vascular system to the point of stenosis in an artery. When thestent is in place, it is expanded to force the artery open to thedesired diameter.

On the other hand, there are some procedures in which stent implants arerequired to constrict the diameter of a blood vessel. For example, Ruizdescribes an endoluminal stent having adjustable constriction in U.S.Pat. No. 6,120,534, whose disclosure is incorporated herein byreference. The stent comprises a deformable mesh having a conicalportion and a constricted region, which forms a flow-limitingconstriction. The stent is delivered and deployed inside a blood vessel.The constricted region of the mesh is then selectively enlarged toadjust the flow impedance in the vessel. Ruiz describes particularly theuse of his, stent to reduce blood flow in the pulmonary artery, as apalliative treatment for infants having complex congenital cardiacmalformations.

Other types of constricting stents and applications of such stents aredescribed by Shalev et al. in PCT Patent Publication WO 01/72239, whosedisclosure is incorporated herein by reference. In particular, thispublication describes the use of a flow-reducing implant in the coronarysinus, in order to promote angiogenesis in the heart tissues. Theimplant is inserted by catheter through a central vein, such as thejugular vein and brought into the coronary sinus. Alternatively, theimplant may be installed in one or more of the coronary veins. Once theimplant is in place, it is allowed to elastically expand or isplastically expanded using a balloon.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a constricting implant thatis simple and inexpensive to manufacture, and can be deployed easily inthe blood vessels, as well as in other body passages. The implantcomprises a pair of generally-cylindrical ring members, which are fixedto a tubular sleeve so as to define a lumen passing through the ringmembers and the sleeve. The ring members each comprise a framework madeof a resilient material, which can be compressed while the implant isinserted into the desired location in the blood vessel, and then expandseither elastically or plastically to roughly the full diameter of thevessel. The sleeve comprises a flexible material, such as a fabric. Thering members are positioned longitudinally along the sleeve so thatthere is a longitudinal gap in between the two ring members. Aconstricting element is fitted around the sleeve in this gap so as toreduce the diameter of the lumen in between the two ring members to lessthan the diameter of the vessel.

Thus, when the implant is inserted into the vessel (or other bodypassage), the ring members expand, along with the portion of the sleeveto which they are fixed. The part of the sleeve in the gap between thering members, however, remains constricted due to the constrictingelement. This constricted area of the lumen typically reduces the flowof blood through the vessel. The implant is particularly useful forrestricting blood flow in the coronary, sinus, as described in theabove-mentioned PCT publication, but it may similarly be used in otherveins and arteries, as well as in other medical applications. In someembodiments, the constricting element may be opened in situ within theblood vessel, so as permit the diameter of the implant to increase ifand when the constriction is no longer desired.

There is therefore provided, in accordance with an embodiment of thepresent invention, a medical implant, including:

first and second ring members, each including a resilient frameworkhaving a generally cylindrical form;

a tubular sleeve, fixed to the first and second ring members so as tohold the ring members in mutual longitudinal alignment, thereby defininga lumen passing through, the ring members; and

a constricting element, which is fit around the sleeve at a locationintermediate the first and second ring members so as to reduce adiameter of the lumen at the location.

The framework may include a wire, which is bent in a serpentine form.Typically, the ring members are adapted to be inserted in aradially-compressed form through a body passage to a target positionwithin the passage, and then to expand radially at the target positionso as to open the lumen therethrough. The framework may include anelastic material, which is compressible to provide theradially-compressed form of the ring members, and which expands radiallywhen released at the target position.

In one embodiment, the implant includes one or more longitudinal supportmembers, fixed to the framework of the first and second ring members,alongside the sleeve, so as to join the first and second ring memberstogether.

In a further embodiment, the sleeve includes a fabric, which is stitchedto the framework of the first and second ring members.

In another embodiment, the lumen passing through the first and secondring members has first and second ends, and the framework is configuredto provide elongate protrusions at one or more of the ends of the lumen.The sleeve may be cut at one or more of the first and second ends inconformance with the protrusions. For example, the sleeve may be cut atthe first end in conformance with the protrusions, while the sleeve atthe second end covers both the protrusions and interstices between theprotrusions at the second end of the lumen.

The implant may be adapted to be implanted in a coronary sinus of apatient, so that a flow of blood through the coronary sinus is inhibitedby the reduced diameter of the lumen.

In another aspect of the invention, the constricting element is adaptedto expand under an outward radial force so as to permit the reduceddiameter of the lumen to increase. In one embodiment, the constrictingelement includes an elastic wire, having bends that are fastened shut soas to provide the reduced diameter, and which are adapted to open underthe outward radial force.

There is also provided, in accordance with an embodiment of the presentinvention, method for producing a medical implant, including:

providing first and second ring members, each including a resilientframework having a generally cylindrical form;

fixing a tubular sleeve to the first and second ring members so as tohold the ring members in mutual longitudinal alignment, thereby defininga lumen passing through the ring members; and

fitting a constricting element around the sleeve at a locationintermediate the first and second ring members so as to reduce adiameter of the lumen at the location.

There is additionally provided, in accordance with an embodiment of thepresent invention, a method for restricting flow of a fluid through abody passage, including:

providing an implant including first and second ring members, eachincluding a resilient framework having a generally cylindrical form,with a tubular sleeve, fixed to the first and second ring members so asto hold the ring members in mutual longitudinal alignment,

passing the implant, in a radially-compressed form, through the bodypassage to a target position within the body passage; and

causing the implant to expand radially at the target position so as toopen the lumen therethrough.

Typically, passing the implant includes enclosing the implant within acatheter, which passes through the body passage, and causing the implantto expand includes ejecting the implant through an aperture in a distalend of the catheter. In some embodiments, the distal end of the catheterhas generally conical shape, and ejecting the implant includes expandingthe distal end so as to open the aperture so that the implant may passtherethrough. Alternatively, ejecting the implant includes tearing thedistal end so as to open the aperture so that the implant may passtherethrough. Further alternatively, the distal end of the catheterincludes an elastic plug, which closes the aperture while the catheterpasses through the body passage, and ejecting the implant includesradially compressing the plug so as to open the aperture and to allowthe lumen of the implant to pass over the plug.

In another aspect of the invention, the method includes exerting anoutward radial pressure from within the implant after the implant hasexpanded in the target position so as to open the constricting element,thereby permitting the reduced diameter of the lumen to increase.Typically, exerting the outward radial pressure includes inserting aballoon into the lumen, and inflating the balloon.

There is further provided, in accordance with an embodiment of thepresent invention, apparatus for delivery of an implant to a targetposition in a body passage, the apparatus including:

an elongate, tubular sheath, which is adapted to be passed through thebody passage while containing the implant in a compressed state insidethe sheath, wherein the sheath has a distal end made of an elasticmaterial in a generally conical shape with an aperture formed therein;and

an ejector, which is adapted to force the implant in a distal direction,thus stretching the elastic material so as to expand the aperture,whereby the implant passes through the aperture.

There is moreover provided, in accordance with an embodiment of thepresent invention, apparatus for delivery of an implant to a targetposition in a body passage, the apparatus including:

an elongate, tubular sheath, which is adapted to be passed through thebody passage while containing the implant in a compressed state insidethe sheath, wherein the sheath has a distal end having a generallyconical shape with an aperture formed therein; and

an ejector, which is adapted to force the implant in a distal direction,thus causing the distal end of the sheath to tear so as to expand theaperture, whereby the implant passes through the aperture.

The distal end of the sheath may be scored with lines, along which thesheath tears.

There is furthermore provided, in accordance with an embodiment of thepresent invention, apparatus for delivery of an implant to a targetposition in a body passage, the apparatus including:

an elongate, tubular sheath, which is adapted to be passed through thebody passage while containing the implant in a compressed state insidethe sheath, wherein the sheath has a distal end with an aperture formedtherein;

a lumen passing longitudinally through the sheath and through theimplant contained within the sheath, such that a portion of the lumen atthe distal end of the sheath, is distended so as to plug the aperturewhile the sheath passes through the body passage, the distended portionof the lumen including a flexible material; and

an ejector, which is adapted to force the implant in a distal direction,thus ejecting the implant through the aperture and compressing thedistended portion of the lumen, so that the implant passes over thelumen to the target position in the body passage.

There is also provided, in accordance with an embodiment of the presentinvention, apparatus for narrowing a body passage, the apparatusincluding:

a narrowing implant, which includes:

first and second ring members, each including a resilient frameworkhaving a generally cylindrical form;

a tubular sleeve, fixed to the first and second ring members so as tohold the ring members in mutual longitudinal alignment, thereby defininga lumen passing through the ring members; and

a constricting element, which is fit around the sleeve at a locationintermediate the first and second ring members so as to reduce adiameter of the lumen at the location; and a catheter for delivering theimplant to a target position in the body passage.

There is additionally provided, in accordance with an embodiment of thepresent invention, a stent for implantation in a lumen, including:

a plurality of struts, with intervening openings therebetween; and

narrow connecting pieces, bridging at least some of the openings so asto interconnect the struts,

wherein exertion of a first outward radial force on the struts causesthe stent to open to a first diameter by opening the interveningopenings between the struts, and

wherein the narrow connecting pieces are adapted to break under,exertion on the struts of a second, outward radial, force, greater thanthe first outward radial force, so that the stent opens to a seconddiameter, greater than the first diameter.

There is further provided, in accordance with an embodiment of thepresent invention, a method for narrowing a blood vessel, including:

inserting a catheter into the blood vessel;

deploying a clip outward from the catheter so that first and second endsof the clip engage respective first and second points on a wall of theblood vessel; and

ejecting the clip from the catheter after the first and second, ends ofthe clip have engaged the first and second points, thus causing the endsof the clip to draw toward one another and thereby pinching together thefirst and second points.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, pictorial view of an implantable device forrestricting flow in a blood vessel, in accordance with an. embodiment ofthe present invention;

FIG. 2 is a schematic, cross-sectional view of the device of FIG. 1,taken along a line II-II;

FIG. 3 is a schematic side view of the device of FIG. 1 implanted in ablood vessel

FIG. 4 is a schematic side view of a device for restricting flow,implanted in a blood vessel, in accordance with another embodiment ofthe present invention;

FIG. 5 is a schematic, pictorial view of an implantable device forrestricting flow in a blood vessel, in accordance with still anotherembodiment of the present invention;

FIGS. 6A and 6B are schematic side views of a catheter used to deliveran implantable device to a target location in a blood vessel, inaccordance with an embodiment of the present invention;

FIGS. 7A and 7B are schematic side views of a catheter used to deliveran implantable device to a target location in a blood vessel, inaccordance with another embodiment of the present invention;

FIGS. 8A, 8B and 8C are schematic side views of a catheter used todeliver an implantable device to a target location in a blood vessel, inaccordance with yet another embodiment of the present invention;

FIG. 9A is a schematic, pictorial illustration of a constricting ring,in accordance with an embodiment of the present invention;

FIGS. 9B and 9C are schematic side views showing details of aconstricting ring, in accordance with embodiments of the presentinvention;

FIG. 10 is a schematic, pictorial illustration of a constricting ringthat has been opened, in accordance with an embodiment of the presentinvention;

FIG. 11 is a schematic, detail view of a stent, in accordance with analternative embodiment of the present invention;

FIG. 12 is a schematic side view of a vascular structure, in which acatheter is inserted for deployment of a constricting clip, inaccordance with an embodiment of the present invention; and

FIGS. 13A-C are schematic, sectional views of the vascular structure ofFIG. 12, taken along a line XIII-XIII in FIG. 12, showing stages in thedeployment of a constricting clip, in accordance with an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to FIGS. 1 and 2, which schematically illustrate adevice 20 for implantation in a body passage, in accordance with anembodiment of the present invention. FIG. 1 is a pictorial illustrationof the device, while FIG. 2 is a cross-sectional view taken along a line11-11 in FIG. 1. Device 20 is adapted for use particularly inrestricting blood flow through the coronary sinus, as described in theabove-mentioned PCT Publication WO 01/72239. Alternatively, devices inaccordance with the principles of the present invention may be implantedelsewhere in the vascular system, as well as in other body passages. Forthe sake of simplicity and clarity, however, and not limitation,embodiments of the present invention are described hereinbelow withreference to implantation of flow-constricting devices in blood vessels,such as the coronary sinus.

Device 20 comprises ring elements 22 and 24, each of which comprises aresilient framework 26. Each framework defines a generally-cylindricalshape, although this shape is distorted by the mechanical constraints ofthe device, as described below. Therefore, the cylinders tend to widenat the ends of device 20 and narrow toward the middle, as shown inFIG. 1. In the pictured embodiments, framework 26 comprises a wire orthin rod, which is bent into a serpentine shape. Typically, theframework comprises an elastic material, which may be compressed orotherwise bent, but then returns to its original shape, as shown in thefigure. Super-elastic materials, such as Nitinol, are useful for thispurpose. Alternatively, the framework may comprise a resilient,deformable material, such as a suitable metal or plastic. Furtheralternatively or additionally, each framework 26 may comprise a mesh orcoil, as is known in the art. In any case, the term “resilient” as usedherein means that once device 20 is deployed within a body passage,framework 26 has sufficient mechanical strength to withstand normalforces exerted by the wall of the passage and by fluid flow within thepassage, in the manner of stents known in the art.

Ring elements 22 and 24 are fixed to a flexible sleeve 28, which has agenerally tubular form. Typically, sleeve 28 comprises a biocompatiblefabric, such as Gore-Tex or Dacron, which is stitched or otherwisefastened to framework 26. Alternatively, other sleeve materials may beused, such as thin plastic or rubber materials. The sleeve is fixed tothe ring elements in such a way as to form a lumen 32 (FIG. 2) throughdevice 20. The sleeve is supported at each end of the lumen by one ofthe ring elements, while leaving a longitudinal gap in, the sleeve,typically several millimeters long, between the inner ends of the tworing elements. While the ring elements themselves are relatively stiff(due to the resilience of framework 26), device 20 can be bent anddeformed freely within the gap region of the sleeve.

A constricting element 30 is fitted around sleeve 28 within the gapregion. As can be seen in FIG. 2, the effect of this constrictingelement is to reduce the diameter of lumen 32 to a predetermined size,less than the expanded diameter of ring elements 22 and 24. Constrictingelement 30 may simply comprise a thread, which is tied around thesleeve, or it may alternatively comprise a closed ring, made of plasticor metal. A constricting ring of this latter type is shown in FIG. 9Aand described hereinbelow with reference thereto.

FIG. 3 is a schematic side view of device 20 after implantation inside ablood vessel 40. Typically, device 20 is passed through the vascularsystem to the appropriate location (such as the coronary sinus), using asuitable percutaneous catheter (not shown in the figures). Suitablemethods of catheterization for this purpose are known in the art. Duringthe insertion procedure, device 20 is compressed radially, so that itsouter diameter is substantially smaller than the blood vessels throughwhich it must pass. As noted above, device 20 is able to bend freely inthe area of the gap between ring elements 22 and 24, where constrictingelement 30 is located. This bending capability generally makes it easierfor the physician operating the catheter to pass the device throughbends in the blood vessels.

Upon reaching the desired location in blood vessel 40, device 20 isreleased from the catheter. If framework 26 is made of an elasticmaterial, such as Nitinol, the device will expand by itself, due to itsown elasticity, as soon as it is released. Alternatively, if framework26 comprises a malleable material, a balloon may be inflated within eachof ring elements 22 and 24, or other means known in the art may be used,in order to expand the framework. The above-mentioned PCT publicationdescribes special types of balloons that may be used for this purpose.As can be seen in FIGS. 1 and 3, the serpentine shape of framework 26creates elongated “fingers” that protrude at the ends of device 20. Oncethe ring elements have expanded, these fingers press outward against thewall of the blood vessel, thus anchoring device 20 in place. Blood invessel 40 flows through lumen 32, but flow is restricted by theconstriction at constricting element 30. If device 2Q is deployed in thecoronary sinus, for example, the flow restriction causes increasedpressure in the coronary veins, thus promoting myocardial angiogenesis.

Device 20 may be left in place indefinitely, in substantially the formshown in FIG. 3. Alternatively, it may be desirable in some cases toeliminate the flow restriction caused, by the device. In such cases, itis not necessary to remove device 20 from the body. Rather, a catheterwith a suitable cutting tool may be inserted percutaneously to thelocation of the device, and the cutting tool may then be used to cutconstricting element 30. The constriction in the diameter of lumen 32will then open up by itself.

FIG. 4 is a schematic side view of an implantable device 50 afterimplantation inside blood vessel 40, in accordance with anotherembodiment of the present invention. Blood in vessel 40 is assumed toflow from left to right in the view of the figure. Device 50 issubstantially identical to device 20, as described above, except for theshape of sleeve 28. In device 20, sleeve 28 is trimmed so that the endsof the sleeve have the same general shape as the “fingers” of framework26. In device 50, however, sleeve 28 is trimmed to a generally straightedge at the upstream (left) end of the device, covering the intersticesbetween the fingers, as well as the fingers themselves. The straightupstream edge can be useful in reducing blood leakage around the sidesof the device, thus providing more complete and reliable flowrestriction. The uneven shape of the sleeve is maintained on thedownstream edge, in order to anchor device 50 securely to the walls ofvessel 40 against the pressure exerted by the blood flow in the vessel.Alternatively, sleeve 28 may be cut in other configurations, as mandatedby medical and mechanical considerations.

FIG. 5 is a schematic, pictorial view of an implantable device 60, inaccordance with still another embodiment of the present invention.Device 60 is also substantially similar to device 20, as describedabove, except for the addition of longitudinal support members 62 and65. The support members join ring elements 22 and 24 together and thusenhance the mechanical strength and stability of device 60. Although twolongitudinal support members are shown in FIG. 5, greater or smallernumbers of supports members may be used in like fashion. Note, however,that in the gap between the ring elements, sleeve 28 is detached fromthe support members, so that the diameter of lumen 32 can still bereduced by constricting element 30.

FIGS. 6A and 6B are schematic side views of a catheter 70, in a cutawayview, which is used to deliver device 20 to a target position in bloodvessel 40, in accordance with an embodiment of the present invention. Asshown in FIG. 6A, catheter 70 has a tubular outer shell 72 and a centrallumen 74. Prior to delivery, device 20 is held inside shell 70, withlumen 74 passing through lumen 32 of device 20. A distal end 76 of shell72 has a roughly conical shape, and has a small exit aperture 78surrounding lumen 32.

Typically, to implant device 20 in vessel 40, an operator threads aguide wire 80 through a part of the patient's vascular system to thetarget position, as is known in the art. For example, the guide wire maybe passed through the jugular vein into the coronary sinus. Once theguide wire is in place, the operator slides lumen 74 over the guidewire, and thus guides distal end 76 of catheter 70 to the targetposition. A contrast medium may be injected through lumen 74 or throughanother, parallel lumen (not shown) to aid the operator in visualizingvessel 40 during the procedure using a fluoroscope, as is known in theart.

When distal end 76 has reached the target position, the operator uses anejector 82 to push device 20 out through aperture 78 in the distal endof the catheter. Distal end 76 in this embodiment is made of a materialthat is sufficiently elastic so that the aperture opens freely to thediameter of device 20. Once the device is ejected, it expands to thediameter of vessel 40, as shown in FIG. 3, and anchors itself in place.The operator then withdraws catheter 70, and distal end 76 contractsback roughly to its original form.

FIGS. 7A and 7B are schematic side views of another catheter 90, whichis used to deliver device 20, in accordance with an alternativeembodiment of the present invention. FIG. 7A shows the catheter beforedelivery of device 20, while FIG. 7B shows the catheter, after, thedelivery. In this embodiment, distal end 76 comprises a thin sheath,which tears open as ejector 82 pushes the device out of the catheter.Optionally, as shown in FIG. 7A, the distal end is scored along lines92, so that as device 20 is ejected, the distal end tears cleanly, in apredictable fashion. Once device 20 has been ejected, the distal end mayremain open where it has torn, but the open distal does not interferewith withdrawal of catheter 90 along wire 80.

FIGS. 8A, 8B and 8C are schematic side views of a catheter 100 fordelivering device 20, in accordance with yet another embodiment of thepresent invention. In this embodiment, distal end 76 has an aperture 102that is large enough to accommodate the (compressed) diameter of device20 when the device is ejected from the catheter. Until the catheterreaches the target position, however, the aperture is closed by adistended portion 104 of a lumen 106 that passes through the catheter,as shown in FIG. 8A. The lumen is typically used to accommodate a guidewire and/or to inject contrast medium, as described above. Distendedportion 104 is made of a flexible material, which may be either elasticor malleable, and is shaped so as to plug aperture 102.

When distal end 76 reaches the target position, lumen 106 is advanced(and/or catheter 100 is withdrawn) so as to open aperture 102, as shownin FIG. 8B. Ejector 82 then pushes device 20 out through the aperture.As shown in FIG. 8C, portion 104 is sufficiently flexible so that as thenarrow, gap region of lumen 32 through device 20 passes over it, portion104 closes down so that lumen 32 can slide over it. Once device 20 hasbeen implanted at the target position, portion 104 resumes its previousshape, and lumen 106 may be pulled back in the proximal direction inorder to close aperture 102. Catheter 100 is then withdrawn from thebody.

FIG. 9A is a schematic, pictorial illustration of a constricting ring120, in accordance with an embodiment of the present invention. Thisring may be used as a constricting element in device 20, taking theplace of element 30 shown in the preceding figures. Ring 120 comprises aflexible, elastic wire 122. For example, wire 122 may comprise asuper-elastic material, such as Nitinol. Wire 122 is formed withmultiple bends, typically in a serpentine pattern, as shown in FIG. 9A.Some of the bends are closed bends 124, at which the wire segments onopposing sides of the bend are fixed together, thus narrowing theoverall circumference of ring 120. When ring 120 is installed in placeof element 30 on device 20, the narrowed circumference of the ringconstricts the diameter of lumen 32, as shown in FIGS. 1 and 2.

FIGS. 9B and 9C are schematic, detail views of one of closed bends 124in ring 120, in accordance with two exemplary embodiments of the presentinvention. In the embodiment of FIG. 9B, the opposing segments of wire122 are pulled together and then fastened by welding, glue or othermeans, at a fastening point 126. Laser micro-welding, as is known in theart, may be used for this purpose. In FIG. 9C, a connecting element 128,such as a miniature ring, is welded or otherwise fastened in placebetween the segments of wire on either side of the bend. In either case,bends 124 are typically closed weakly enough so that the fasteningpoints or connecting elements will break open under outward radialpressure.

FIG. 10 is a schematic, pictorial illustration of ring 120 followingopening of closed bends 124, in accordance with an embodiment of thepresent invention. The closed bends may be opened in situ, after device20 has been implanted in a blood vessel. For this purpose, for example,a balloon catheter may be inserted into lumen 32 of device 20, and theballoon may be inflated with sufficient pressure to break open thefastening points of at least some of bends 124. Due to the elasticity ofwire 122, ring 120 will then expand to the larger diameter shown in FIG.10, and lumen 32 will open up accordingly. This sort of procedure may beused, for example, to permit free flow of blood through vessel 40 whenthe constriction due to device 20 is no longer needed or desired.

FIG. 11 is a schematic, detail view of a part of a stent 130, inaccordance with another embodiment of the present invention. Thisembodiment also uses the principle of radial expansion of anintravascular implant that was described above. Stent 130 comprises astructure of struts 132 with intervening openings 134. Some of theopenings are bridged by narrow connecting pieces 136. Stent 130 isinitially collapsed and crimped over a balloon for insertion into thetarget blood vessel. Inflation of the balloon to a first, intermediatepressure causes the stent to expand radially outward, so that openings134 between struts 132 open to the configuration shown in FIG. 11. Theballoon is then withdrawn. The stent may be used in this configuration,for example, to open a blocked artery or other body lumen.

It often occurs after implantation of a stent that the body lumen inquestion once again becomes constricted, due to accretion of materialinside the stent, for example. In this case, a balloon may once more beinserted inside stent 130 and inflated to a second, higher pressure. Theballoon thus exerts an outward radial force on stent 130, causing one ormore of connecting pieces 136 to break open. Thus, the diameter of stent130 (and of the lumen it is supporting) is increased simply and safely.

Although in the embodiments described above, framework 26 and sleeve 28are shown to have certain particular shapes, alternative shapes andforms of these elements, which will, be apparent to those skilled in theart, are considered to be within the scope of the present invention.Similarly, catheters of the general types described above may be used todeliver not only device 20, but also other implantable devices asdescribed hereinabove and as are otherwise known in the art. On theother hand, although the catheters shown here provide convenient meansfor delivering implants in accordance with the present invention, suchimplants may also be delivered by other means, both minimally invasive(typically percutaneous) and invasive (i.e., surgical).

Methods for reducing the diameter or circumference of a vascularstructure by surgical means are also known in the art. Methods of thissort are described, for example, in, U.S. Pat. No. 5,593,424 and U.S.Pat. No. 6,561,969, whose disclosure are incorporated herein byreference. These methods generally require suturing of the vasculartissue, which can be difficult and time-consuming to carry out.

In contrast to these methods and to the preceding embodiments, FIG. 12schematically illustrates a method for constricting the diameter of avascular structure without the use of sutures or a stent, in accordancewith an alternative embodiment of the present invention. The embodimentis illustrated here with reference to reducing the diameter of acoronary sinus 140 of a patient, although this method is also applicableto other vascular structures. A catheter 142 is inserted through a rightatrium 144 of the patient into coronary sinus 140. The catheter is bentat its distal end, as shown in the figure, to permit convenientdeployment of a constricting clip 146, as described below.

FIGS. 13A-C are schematic, sectional views of coronary sinus 140, takenalong a line XIII-XIII in FIG. 12, showing stages in the deployment ofclip 146, in accordance with an embodiment of the present invention.Clip 146 typically comprises a super-elastic material, which is formedso that in its relaxed state, it has an approximately closed form, asshown in FIG. 13C, for example. During insertion of catheter 142 intothe coronary sinus, however, clip 146 is compressed within the distalend of catheter 142, as shown in FIG. 13A.

Once catheter 142 has been advanced into coronary sinus 140, adeployment mechanism, such as a pusher (not shown) inside the catheter,is actuated in order to advance clip 146 out of the distal end of thecatheter. As a result, the clip opens up into the configuration shown inFIG. 13B. Ends 148 of the clip catch the tissue of coronary sinus 140 attwo points that are spaced apart on the wall of the coronary sinus. Theelasticity of clip 146 causes the ends of the clip to draw together asthe clip is advanced further out of the catheter, as illustrated byarrows 150. Finally, when the clip has advanced completely out of theend of the catheter, ends 148 close in toward one another and pinchtogether the portion of the vascular tissue that is located between theclip ends. The result, as seen in FIG. 13C, is that the effectivediameter of coronary sinus 140 is reduced.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsubcombinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art.

1. A medical implant, comprising: first and second ring members, eachincluding a resilient framework having a generally cylindrical form; anda tubular segment, fixed to the first and second ring members so as tohold the ring members in mutual longitudinal alignment, thereby defininga lumen passing through, the ring members.